AML-392 Treatment of Blastic Plasmacytoid Dendritic Cell Neoplasm in Pediatric Patients With Tagraxofusp, a CD123-Targeted Therapy

Context: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive hematologic malignancy that primarily affects older adults, with pediatric patients making up 10%–20% of all cases. The rarity of BPDCN in the pediatric population makes collecting robust safety and efficacy data challenging, and there is a paucity of data published for pediatric patients. Tagraxofusp (TAG, SL-401) targets CD123, a molecule that is overexpressed in all cases of BPDCN, and is the only approved drug for treatment of adult and pediatric patients with BPDCN. Objective: To further expand the safety and efficacy data of TAG therapy in pediatric/young adult patients with newly diagnosed (1L) or relapsed/refractory (R/R) BPDCN. Design: Multicenter retrospective collation of case reports. Data were collated and summarized descriptively. Setting: A total of 6 cancer centers across the US and Europe. Patients: Data were collected from pediatric/young adult patients with BPDCN who received TAG during their course of treatment. Intervention(s): All patients received 12 mcg/kg TAG, while 1 patient also received 7 mcg/kg TAG at second relapse. Main Outcome Measure(s): Safety was assessed via monitoring of adverse events (AEs) and laboratory abnormalities. Efficacy was evaluated through tumor responses and survival. Results: Eight pediatric patients (n=5, 1L; n=3, R/R) were included. The median age was 15.5 years (range 2–21), and 7 of the 8 patients were female. The median number of TAG cycles was 3.5 (range 1–4). All AEs occurred during cycle 1. One patient experienced grade 2 capillary leak syndrome, which was treated and resolved. Two patients experienced hypoalbuminemia, 2 had transaminitis, and 1 experienced headache, all of which were manageable. Three patients reported no AEs. Three 1L patients achieved a complete response, including 1 patient with extensive disease (skin, bone marrow, and central nervous system involvement). Five patients (n=3, 1L; n=2, R/R) were bridged to stem cell transplant (SCT) and 7 patients are alive at the time of publication. Conclusions: TAG demonstrated promising antitumor efficacy in pediatric/young adult patients with BPDCN, enabling 75% of this pediatric cohort to be bridged to SCT. TAG had a manageable safety profile, similar to that reported for adults.